In the processing of tubular knitted fabric, such as in the spreading to width or finish calendering treatment of the fabric, it is conventional practice to direct the tubular fabric over an internal spreading device. This device, often referred to as a spreader or propeller, distends the fabric laterally to a predetermined uniform width, typically advancing the fabric by means of longitudinally moving belts engaging the inner edge walls of the fabric. While the fabric is held in its laterally distended condition, and while it is being advanced through the finishing equipment, it is subjected to a steaming operation, to relax the fibers and enable the fabric to readjust to its laterally distended, geometrically uniform condition. To a large extent, the fabric then tends to retain this geometrical condition as it is delivered at the discharge end of the spreading device. When the finishing operation includes calendering, the thus spread and steamed fabric is passed directly between a pair of calender rolls, and subsequently gathered as by folding or rolling.
Heretofore, in a fabric processing operation as described above, the overall rate of production has been limited by the ability effectively to impart steam into the fabric, to achieve the necessary fiber lubrication, relaxation and overall fabric stabilization. In this connection, merely increasing the rate of application of steam to the fabric, as by increasing steam pressure or the like, has not proven to be an effective way of increasing the overall fabric production. Thus, with conventional procedures, when an effort is made simply to increase the rate of steam application, the operator is faced with serious problems of water condensation on the fabric and on the machinery. When this occurs, the fabric becomes stained by water spots, resulting in a serious loss of quality, which may more than offset any increase in production rate. This problem has existed notwithstanding the utilization of so-called dripless steam discharge boxes, because the volumes of steam are such as to give rise to unwanted condensation problems after the steam has been issued from the steam boxes.
In accordance with the invention, a pair of steam boxes of known design are mounted in opposed relation on opposite sides of the plane of the fabric being conveyed by the spreader. The steam boxes have discharge slots facing the fabric, such that high velocity jets of steam are directed in opposed relation toward the plane of the passing fabric, in a generally well known manner. Significantly higher production capabilities are imparted to this otherwise conventional configuration by closely (1) embracing and confining the steam in a substantially enclosed steam chamber through which the fabric passes while engaged by the fabric spreader, and (2) causing the confined steam to be exhausted downwardly from the enclosed chamber.
The specific proportions of the enclosing steam chamber are not known to be critical. However, it is consistent with the invention that there be a relative minimum of chamber volume above and below the steamers, with most of the open chamber volume being located immediately upstream and immediately downstream of the steam boxes. Further, the dimension of the steam chamber in the direction of fabric movement is significantly less than the length of the fabric spreader, permitting the spreader to extend entirely through the otherwise enclosed steam chamber.
To accommodate the passing through the steam chamber of the fabric spreader, which may be adjusted to various widths to suit the requirements of the fabric being processed, the steamer apparatus of the invention includes sealing elements at the entry and exit openings of the steam chamber. In one embodiment of the invention, the sealing means are in the form of flexible brush-like elements arranged to conform about the spreading device and fabric without applying any significant amount of pressure thereto, to assist in the confinement of the steam in the enclosed chamber while at the same time avoiding any pressure marking of fabric.
In another embodiment of the invention, a novel form of width-adjustable sealing elements is provided. These sealing elements may be easily moved between active and retracted positions, to enlarge or narrow the entry and exit openings of the chamber as appropriate. To advantage, the width-adjustable seals do not contact the fabric.
For most effective results, the steam chamber should be provided with its own exhaust system arranged to effect removal of the excess steam at a rate somewhat corresponding to the rate of steam discharge into the chamber, while providing for a neutral or slightly positive pressure within the chamber. Pursuant to the invention, the exhaust arrangement provides for the downward flow of the exhausting steam from regions adjacent the entry and discharge openings of the chamber, enabling highly efficient utilization of the steam to be realized. This desired operation is achieved by providing an exhaust outlet in the bottom of the chamber in conjunction with a transversely extending baffle arrangement which forms, in effect, a false bottom in the lower portion of the chamber.
The steam chamber advantageously is provided along the upper edges of the entry and exit openings with condensation collecting gutters, associated with downwardly sloping upper walls. This construction and configuration avoids condensation spotting of the fabric during the start-up phases of operation, thus avoiding the need for a substantial warm-up period.